No description available.

<p>This study was made as a part of a feasibility study on a polishing wetland at Rimbo wastewater plant (wwp) in Norrtälje municipality. The wwp had to decrease the nitrogen discharge to reach the limit 15 mg tot-N/l. The nitrogen in the outlet was mainly in the form of nitrate, hence the wetland mainly ought to support denitrification. The proposed area for the wetland was situated right next to the wwp and was already in the municipalitys posession. One aim of this study was to examine what spieces of plants needed to achieve highest possible denitrification. Some different plant spieces for providing a good and interesting environment for birds and people were also proposed. Furthermore a massbalance model was developed for studying the important exchange processes in a wetland, to study the impact of an uneven streambed on the hyporheic water exchange and for trying to predict the wetlands nitrogen removal capacity. Proposed plants to support denitrification was different reeds such as Common reed (Phragmites australis), Bulrush (Typha), Reed Sweet-grass (Glyceria maxima) och Reed Canry-grass (Phalaris Arundinacea). Common reed is a durable species who can survive in deeper water up to 2 metres while the others need a shallower water about 0,5 m of depth. For the good of the birdlife, different spieces of Sedges (Carex) were chosen due to their ability to produce large amounts of nutrient rich seeds. Measurment in sediment cores from Ekeby wetland in Eskilstuna gave a potential denitrification capacity of 3,31 mg NO3-N m^-3 _sed s^-1. The denitrification capacity was then used in a massbalance model were the theory of advective pumping in an uneven bedsurface also was implemented. Evaluation of the model results showed that an uneven bedsurface did not contribute to an increased nitrogen removal from the wetland, possibly due to a far too low advection and flow of the water. This was also a reason to why the distribution between denitrification from the water- and plant community vs the sediment was unbalanced. The model results showed that less than 1 % of the reduced nitrogen came from the sediment part, in contrast to current knowledge that says about 50%. The model and the participating exchange processes need to be further evaluated before the models prediction of nitrogen removal can be used in design of a wetland. Calculations and comparisons with other wetlands showed that with a well estimated, grown up and maintained wetland, there should be no problems in achieving the goal of nitrogen removal in Rimbo wetland. Such a wetland should also provide a good habitat for birds and animals and also be a good recreationarea for people to visit, properties that were appreciated as important effects in other wetlands studied in this work.</p> / <p>Detta arbete gjordes som en del av en förstudie för anläggande av en efterpolerande våtmark till reningsverket i Rimbo, Norrtälje kommun. Reningsverket behövde sänka sitt utsläpp av kväve till riktvärdet 15 mg tot-N/l. Huvuddelen av kvävet i utloppsvattnet förelåg i nitratform, varför denitrifikationen borde förstärkas genom att anlägga en våtmark. Det tilltänkta området för våtmarken ligger i anslutning till reningsverket och ägs idag av kommunen. I detta arbete undersöktes vilken växtlighet i våtmarken som var lämpligast för syftet att få en så bra denitrifikation som möjligt. Även olika växtarter för att ge en intressant miljö för fåglar och människor togs fram. Dessutom utvecklades en massbalansmodell som användes för att studera de utbytesprocesser som är viktiga i en våtmark, frågan hur en ojämn bottenmorfometri påverkar det hyporheiska vattenutbytet samt om det går att förutsäga reningskapaciteten i Rimbo våtmark. Lämpliga växter för denitrifikationen ansågs vara vassbildande växter, och då främst främst bladvass (Phragmites australis), men även kaveldun (Typha), jättegröe (Glyceria maxima) och rörflen (Phalaris Arundinacea). Bladvass är en mycket tålig växt som klarar stort vattendjup, medan de andra vassorterna behöver en grundare våtmark på ca 0,5 m. För fågellivets bästa ansågs starrväxter (Carex) vara viktiga arter då de producerar stora mängder frön. Mätning av denitrifikationspotentialen i sediment från Ekeby våtmark gav en hastighet för denitrifikationen i sedimentet på 3,31 mg NO3-N m^-3 _sed s^-1. Denitrifikationen från sediment användes sedan i en massbalansmodell där även även teorin om advektivt pumputbyte vid ojämn bottenform implementerades. En utvärdering av modellresultaten kunde avgöra att en ojämn eller vågig bottenmorfometri inte skulle förbättra reningen i våtmarken. Detta beroende på bland annat för låg advektionshastighet och flöde. Detta låga flöde ned i sedimentet bidrog även till att fördelningen av kväveborttag från sediment respektive vatten- och växtdelen blev snedfördelad. Enligt modellen var det mindre än 1% av kvävet som togs bort från sedimentet medan all vetenskap tyder på närmare 50%. Modellen och de ingående utbytesprocesserna bör utvärderas och utvecklas ytterligare innan den kan användas som verktyg för att beräkna kvävereningen från en våtmark. Beräkningar och jämförelser med andra våtmarker visade dock att en väl beväxt, utförd och beskickad våtmark inte skulle ha några problem att sänka nitrathalten till riktvärdet. En våtmark skulle även utgöra en bra uppehållsmiljö för fåglar, djur och människor vilket anses som viktiga mervärden i våtmarker på andra platser i Sverige.</p>

<p>The objective of this thesis is to improve the understanding of what processes and mechanism affects the distribution of polychlorinated biphenyls (PCBs) and organic carbon in coastal sediments. Because of the strong association of hydrophobic organic contaminants (HOCs) such as PCBs with organic matter in the aquatic environment, these two entities are naturally linked. The coastal environment is the most complex and dynamic part of the ocean when it comes to both cycling of organic matter and HOCs. This environment is characterised by the largest fluxes and most diverse sources of both entities. A wide array of methods was used to study these processes throughout this thesis. In the field sites in the Stockholm archipelago of the Baltic proper, bottom sediments and settling particulate matter were retrieved using sediment coring devices and sediment traps from morphometrically and seismically well-characterized locations. In the laboratory, the samples have been analysed for PCBs, stable carbon isotope ratios, carbon-nitrogen atom ratios as well as standard sediment properties. From the fieldwork in the Stockholm Archipelago and the following laboratory work it was concluded that the inner Stockholm archipelago has a low (≈ 4%) trapping efficiency for freshwater-derived organic carbon. The corollary is a large potential for long-range waterborne transport of OC and OC-associated nutrients and hydrophobic organic pollutants from urban Stockholm to more pristine offshore Baltic Sea ecosystems.</p><p>Theoretical work has been carried out using Geographical Information Systems (GIS) and statistical methods on a database of 4214 individual sediment samples, each with reported individual PCB congener concentrations. From this work it was concluded that the continental shelf sediments are key global inventories and ultimate sinks of PCBs. Depending on congener, 10-80% of the cumulative historical emissions to the environment are accounted for in continental shelf sediments. Further it was concluded that the many infamous and highly contaminated surface sediments of urban harbours and estuaries of contaminated rivers cannot be of importance as a secondary source to sustain the concentrations observed in remote sediments. Of the global shelf PCB inventory < 1% are in sediments near population centres while ≥ 90% is in remote areas (> 10 km from any dwellings). The remote sub-basin of the North Atlantic Ocean contains approximately half of the global shelf sediment inventory for most of the PCBs studied.</p>

This thesis examines the processes of longshore sediment transport in the swash zone of a mixed sand and gravel shoreline, Lake Coleridge, New Zealand. It focuses on the interactions between waves and currents in the swash zone and the resulting sediment transport. No previous study has attempted to concurrently measure wave and current data and longshore sediment transport rates on a mixed sand and gravel lakeshore beach in New Zealand. Many of these beaches, in both the oceanic and lacustrine environments, are in net long-term erosion. It is recognised that longshore sediment transport is a part of this process, but very little knowledge has existed regarding rates of sediment movement and the relationships between waves, currents and swash activity in the foreshore of these beach types. A field programme was designed to measure a comprehensive range of wind, wave, current and morphological variables concurrently with longshore transport. Four electronic instruments were used to measure both waves and currents simultaneously in the offshore, nearshore and swash zone. In the offshore area, an InterOcean S4ADW wave and current meter was installed to record wave height, period, direction and velocity. A WG-30 capacitance wave gauge measured the total water surface variation. A pair of Marsh-McBirney electromagnetic current meters, measuring current directions and velocities were installed in the nearshore and swash zone. Data were sampled for 18 minutes every hour with a Campbell Scientific CR23x data-logger. The wave gauge data was sampled at a rate of 10 Hz (0.1 s) and the two current meters at a rate of 2 Hz (0.5 s). Longshore sediment transport rates were investigated with the use of two traps placed in the nearshore and swash zone to collect sediment transported under wave and swash action. This occurred concurrently with the wave measurements and together yielded over 500 individual hours of high quality time series data. Important new insights were made into lake wave processes in New Zealand's alpine lakes. Measured wave heights averaged 0.20-0.35 m and ranged up to 0.85 m. Wave height was found to be strongly linked to the wind and grew rapidly to increasing wind strength in an exponential fashion. Wave period responded more slowly and required time and distance for the wave length to develop. Overall, there was a narrow band of wave periods with means ranging from 1.43 to 2.33 s. The wave spectrum was found to be more mixed and complicated than had previously been assumed for lake environments. Spectral band width parameters were large, with 95% of the values between 0.75 and 0.90. The wave regime attained the characteristics of a storm wave spectrum. The waves were characteristically steep and capable of obtaining far greater steepness than oceanic wind-waves. Values ranged from 0.010 to 0.074, with an average of 0.051. Waves were able to progress very close to shore without modification and broke in water less than 0.5 m deep. Wave refraction from deep to shallow water only caused wave angles to be altered in the order of 10%. The two main breaker types were spilling and plunging. However, rapid increases in beach slope near the shoreline often caused the waves to plunge immediately landward of the swash zone, leading to a greater proportion of plunging waves. Wave energy attenuation was found to be severe. Measured velocities were some 10 times less at two thirds the water depth beneath the wave. Mean orbital velocities were 0.30 m s⁻¹ in deep water and 0.15 m s⁻¹ in shallow water. The ratio difference between the measured deep water orbital velocities and the nearshore orbital velocities was just under one half (us/uo = 0.58), almost identical to the predicted phase velocity difference by Linear wave theory. In general Linear wave theory was found to provide good approximations of the wave conditions in a small lake environment. The swash zone is an important area of wave dissipation and it defines the limits of sediment transport. The width of the swash zone was found to be controlled by the wave height, which in turn determined the quantity of sediment transported through the swash zone. It ranged in width from 0.05 m to 6.0 m and widened landward in response to increased wave height and lakeward in response the wave length. Slope was found to be an important secondary control on swash zone width. In low energy conditions, swash zone slopes were typically steep. At the onset of wave activity the swash zone becomes scoured by swash activity and the beach slope grades down. An equation was developed, using the wave height and beach slope that provides close estimates of the swash zone width under a wide range of conditions. Run-up heights were calculated using the swash zone width and slope angle. Run-up elevations ranged from 0.01 m to 0.73 m and were strongly related to the wave height and the beach slope. On average, run-up exceeds the deep water wave height by a factor of 1.16H. The highest run-up elevations were found to occur at intermediate slope angles of between 6-8°. Above 8°, the run-up declined in response to beach porosity and lower wave energy conditions. A generalised run-up equation for lake environments has been developed, that takes into account the negative relationship between beach slope and run-up. Swash velocities averaged 0.30 m s⁻¹ but maximum velocities averaged 0.98 m s⁻¹. After wave breaking, swash velocities quickly reduced through dissipation by approximately one half. Swash velocity was strongly linked to wave height and beach slope. Maximum velocities occurred at beach slopes of 5°, where incident swash dominated. At slopes between 6° and 10°, swash velocities were hindered by turbulence, but the relative differences between the swash and backswash flows were negligible. At slope angles above 10° there was a slight asymmetry to the swash/backswash flow velocities due to beach porosity absorbing water at the limits of the swash zone. Three equations were developed for estimating the mean and maximum swash velocity flows. From an analysis of these interactions, a process-response model was developed that formalises the morphodynamic response of the swash zone to wave activity. Longshore sediment transport occurred exclusively in the swash zone, landward of the breaking wave in bedload. The sediments collected in transit were a heterogeneous mix of coarse sands and fine-large gravels. Hourly trapped rates ranged from 0.02 to 214.88 kg hr⁻¹. Numerical methods were developed to convert trapped mass rates in to volumetric rates that use the density and porosity of the sediment. A sediment transport flux curve was developed from measuring the distribution of longshore sediment transport across the swash zone. Using numerical integration, the area under this curve was calculated and an equation written to accurately estimate the total integrated transport rates in the swash zone. The total transport rates ranged from a minimum of 1.10 x 10-5 m³ hr⁻¹ to a maximum of 1.15 m³ hr⁻¹. The mean rate was 7.36 x 10⁻² m³ hr⁻¹. Sediment transport was found to be most strongly controlled by the wave height, period, wave steepness and mean swash velocity. Transport is initiated when waves break at an oblique angle to the shoreline. No relationships could be found between the grain size and transport rates. Instead, the critical threshold velocities of the sediment sizes were almost always exceed in the turbulent conditions under the breaking wave. The highest transport rates were associated with the lowest beach slopes. It was found that this was linked to swash high velocities and wave heights associated with foreshore scouring. An expression was developed to estimate the longshore sediment transport, termed the LEXSED formula, that divides the cube of the wave height and the wave length and multiplies this by the mean swash velocity and the wave approach angle. The expression performs well across a wide range of conditions and the estimates show very good correlations to the empirical data. LEXSED was used to calculate an accurate annual sediment transport budget for the fieldsite beaches. LEXSED was compared to 16 other longshore sediment transport formulas and performed best overall. The underlying principles of the model make its application to other mixed sand and gravel beaches promising.

The intensive research on sediment transport indicates a need of an appropriate equation for predicting the total sediment load in rivers to manage reservoirs, operate dam and design in-stream hydraulic structures. None of the available equations in sediment transport has gained universal acceptance for predicting the total sediment transport rate. These facts indicate the need of a general formula to represent all these formula for predicting the sediment transport rate. The first goal of this dissertation is to find a unified total sediment transport equation for all rivers. On the other hand, scour around hydraulic structures such as spur dikes and bridge piers can be a serious problem that weakens structural stability. An investigation on the turbulent flow field and turbulence distribution around such hydraulic structures is essential to understand the mechanism of local scour and to determine which turbulence properties affect the local sediment transport. In addition, a universal turbulent model that is valid for all cases of turbulent flow in open channels does not exist. This dissertation thoroughly examined the turbulent flow field and turbulence distribution around a series of three dikes. The goal is to determine the significant turbulent properties for predicting the local sediment transport rate and to identify the appropriate turbulence model for simulating turbulent flow field around the dikes.To develop a general unified total load equation, this study evaluates 31 commonly used formulae for predicting the total sediment load. This study attributes the deviations of calculated results from different formulae to the stochastic properties of bed shear stresses and assumes that the bed shear stress satisfies the log- normal distribution. At any given bed shear stress, Monte Carlo simulation is applied to each equation, and a set of bed shear stresses are randomly generated. Total sediment load generated from each Monte Carlo realization of all the equations are assembled to represent the samples of total sediment load predicted from all the equations. The statistical properties of the resultant total sediment loads (e.g. standard deviation, mean) at each given bed shear stress are calculated. Then, a unified total sediment load equation is obtained based on the mean value from all the equations. The results showed the mean of all the equations is a power function of dimensionless bed shear stress. Reasonable agreements with measurements demonstrate that the unified equation is more accurate than any individual equation for predicting the total sediment load.An experimental study and numerical simulation of the flow field and local scour around a series of spur dikes is performed in a fixed flat bed and scoured bed condition. A micro-Acoustic Doppler Velocimeter (ADV) is used to measure the instantaneous velocity field in all the three spatial directions and the measured velocity profiles are used to calculate the turbulence properties. Results show that the local scour develops around the first dike. Turbulence intensity together with the mean velocity in the vertical direction measured at the flat bed closely correlates to the scour depth. In addition, the maximum bed shear stress, occurring at the tip of the second dike in the three-dike series, does not correspond to the maximum scour. Large bed load transport due to bed shear stress may not initiate bed scouring, but turbulence bursts (e.g. sweeps and ejections) will entrain sediment from bed surface and develop the local scour.A three-dimensional numerical model FLOW-3D is used to simulate the turbulent flow field around a series of spur dikes in flat and scoured bed. This study examines Prandtl's mixing length model, one equation model, standard two-equation model, Renormalization-Group (RNG) model, and Large Eddy Simulations (LES) turbulence model. The Prandtl's mixing length model and one equation model are not applicable to flow field around dikes. Results of mean flow field by using the standard two-equation model, and RNG turbulence model are close to the experimental data, however the simulated turbulence properties from different turbulent model deviate considerably. The calculated results from different turbulence models show that the RNG model best predicts the mean flow field for this series of spur dikes. None of the turbulence closure models can predict accurate results of turbulence properties, such as turbulence kinetic energy. Based on those results, this study recommends the use of RNG model for simulating mean flow field around dikes. Further improvements of FLOW-3D model is needed for predicting turbulence properties near this series of spur dikes under various flow conditions.

Numerical model for simulating sediment transport in unsteady flow is incomplete in several aspects: first of all, the numerical schemes have been proved suitable for the simulation of flow over rigid bed needs to be reevaluated for unsteady flow over mobile bed; secondly, existing non-equilibrium sediment transport models are empirically developed and therefore lack of consistency regarding the evaluation of the non-equilibrium parameters; thirdly, the sediment transport in various applications have unique features which needs to be considered in the models. Sediment transport in unsteady flows was studied using analytical and numerical methods. A one dimensional (1D) finite volume method (FVM) model was developed. Five popular numerical schemes were implemented into the model and their performances were evaluated under highly unsteady flow condition. A novel physically-based non-equilibrium sediment transport model was established to describe the non-equilibrium sediment transport process. Infiltration effects on flow and sediment transport was included to make the model applicable to simulate irrigation induced soil erosion in furrows. The Laursen (1958) formula was adopted and modified to calculate the erodibility of fine-grain sized soil, and then verified by laboratory and field datasets. The numerical model was applied to a series of simulations of sediment transport in highly unsteady flow including the dam break erosional flow, flash flood in natural rivers and irrigation flows and proved to be applicable in various applications. The first order schemes were able to produce smooth and reasonably accurate results, and spurious oscillations were observed in the simulated results produced by second order schemes. The proposed non-equilibrium sediment transport model yielded better results than several other models in the literatures. The modified Laursen (1958) formula adopted was applicable in calculating the erodibility of the soil in irrigation. Additionally, it was indicated that the effect of the jet erosion and the structural failure of the discontinuous bed topography cannot be properly accounted for due to the limitation of 1D model. The comparison between the simulated and measured sediment discharge hydrographs indicated a potential process associated to the transport of the fine-grain sized soil in the irrigation furrows.

Sedimentary deposits have been broadly used to constrain past climate change and tectonic histories within mountain belts. This dissertation summarizes three studies that evaluate the effects of climate change and tectonics on sedimentary basin development. (1) The paleoslope estimation method, a method for calculating the threshold slope of a fluvial deposit, does not account for the stochastic variations in water depth in alluvial channels caused by climatic and autogenic processes. Therefore, we test the robustness of applying the paleoslope estimation method in a tectonic context. Based on our numerical modeling results, we conclude that if given sufficient time gravel can prograde long distances at regional slopes less than the minimum transport slope calculated with the paleoslope estimation method if water depth varies stochastically in time, and thus, caution should be exercised when evaluating regional slopes measured from the rock record in a tectonic context. (2) The role of crustal thickening, lithospheric removal, and climate change in driving surface uplift in the central Andes in southern Bolivia and changes in the creation of accommodation space and depositional facies in the adjacent foreland basin has been a topic of debate over the last decade. Our numerical modeling results show that gradual rise of the Eastern Cordillera above 2-3 km prior to 22 Ma leads to sufficient sediment accommodation for the Oligocene-Miocene foreland basin stratigraphy, and thus, the Eastern Cordillera gained the majority of its modern elevation prior to 10 Ma. Also, we conclude that major changes in grain size and depositional rates are primarily controlled by mountain-belt migration (i.e., climate change and lithospheric removal are secondary mechanisms). (3) Existing equations for predicting the long-term bedload sediment flux in alluvial channels include mean discharge as a controlling variable but do not explicitly include variations in discharge through time. We develop an analytic equation for the long-term bedload sediment flux that incorporates both the mean and coefficient of variation of discharge. Our results show that although increasing aridity leads to an increase in large discharges with respect to small discharges, long-term bedload sediment transport rates decrease for both gravel and sand-bed rivers with increasing aridity.

No description available.

High-resolution physical and biogeochemical field data in central Lake Erie during the summers of 2008-2009 along with a three-dimensional numerical model were used to investigate the dynamics of basin scale waves and sediment resuspension mechanisms. In Chapter 2, the modal response of the Poincaré waves in the lake is assessed. The vertical mode-one Poincaré wave was found to be mostly dominant during the seasonal stratified period. The horizontal modal structure was also investigated in a sensitivity analysis, using the numerical model forced with real and idealized wind events. In Chapter 3, dynamics of bottom mixed layer (BML), primarily forced in the outer layer by surface seiches and Poincaré waves is studied for two 10-days representative intervals of weak and strong stratification. Shear velocity was calculated by least square fitting the well-known law-of-the-wall equation to observed near-bed velocity in a region of constant shear stress. Height of the BML is computed using water density (from water temperature) and compared with heights of logarithmic layer approximated using the law-of-the-wall equation and its modified form with buoyancy length scale term. Published equations for estimating BML heights are evaluated and modified for the lake. In Chapter 4, we investigate physical processes leading to sediment resuspension in the lake including surface waves (periods of 4-8s), up/downwelling events (periods of 3-4 day), and high frequency internal waves (periods of 5-45min). Temporal changes in near-bottom sediment resuspension are illustrated using changes in acoustic backscatter signals from current profilers and time series of turbidity measurements to identify the mechanism responsible for sediment resuspension. Resuspension is parameterized as a function of the critical velocity ~0.25ms-1 and from surface waves using linear wave theory. Finally, based on the critical velocity and sediment grain size analysis (from in-site field data), critical shear stress and Shields parameter are calculated and compared with previous observations in Lake Erie and in other locations suggesting a modified Shields diagram for silty bed materials. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2012-12-19 20:54:15.832

The influence of channel morphology and hydraulics on sediment transport within steep upland streams is investigated. Step-pools are the most common bedform in such streams. Bedload transport processes operating in a perennial step-pool stream in central England are established using magnetically-tagged particles and bedload pit samplers. Water-surface slope in two step-pool streams is monitored in detail. Water-surface slope measurements show that step-pool bedforms cause large spatial variations in flow depth during floods, and that the temporal variation of watersurface slope during a flood wave differs diametrically from the pattern found in lowgradient rivers that have little roughness. These results demonstrate that it is difficult to estimate the forces acting on the streambed in steep, rough streams and, therefore, conventionally established flow variables cannot be used to predict bedload transport . rates in step-pool channels. Particle tracing experiments are used to determine the control that step-pool morphology and flow hycfraulics have on particle displacements. Step-pool streams exhibit smaller particle travel distance per flood event than low-gradient rivers. This difference reflects the greater flow resistance and bed rugosity of step-pool streams. Bed morphology dictates flood particle displacement at step-pool bedform scale. It is shown that entrainment, pool export rates and transport distances of coarse sediment are dependent on downstream step dimensions, step permeability and pool form. Large variations in bedload transport rates at any given flow strength are associated with variable sediment supply, and particle tracing demonstrates that sediment availability is controlled at unit pool scale. Bedload consists of fine gravel moving over a stable bed surface at low discharges, while, at higher discharges, bedload coarsens, approaching the size of the pool bed material as the bed surface is partially mobilized. Step framework clasts are stable features of the streambed. Results from this study are incorporated into a descriptive model of discharge-related bedload transport phases in step-pool streams.